92SierraSLE

I recently posted about an LQ4 that I sourced from a junkyard. My original question was concerning a watermark visible in cylinder 8. General consensus was that I should be fine deglazing with a ball hone and re-ringing. Several folks recommended dropping off the block to a machine shop for cleaning and to have new cam bearings installed. Another recommendation was to mic the cylinders for taper and out of roundness. I’ve done some reading since then and managed to pick up a few new tools, a bore gauge and micrometer set, and obtained some measurements.

I would like to hear your thoughts on whether I should proceed with my original plan of deglazing and re-ringing or have it bored 0.030 over. Note, measurements were taken with pistons in place as I’m still not 100% sure the bottom end needs to be taken apart. Pistons were moved to the bottom of their travel for the bottom measurement. I know it’s not ideal but figured it would at least provide a good idea of what I’m facing.

This is all that I was able to find regarding acceptable oversize ranges for the LQ4: 4.0007 - 4.0014. This information is out of a service manual which I’d assume takes customer satisfaction into account (avoiding returning unhappy customers). I’m obviously not a professional mechanic working on someone else's car, this project is intended for use around town and overall fun. With that said, most if not all Thrust side measurements exceed 4.0014, the largest being top measurement of cylinder 8 at 0.0035.

The goal is 400-450hp + 150 shot.

PS - I was 90% sold on having it bored and avoiding potential headaches but research on cost of remaining items needed for the build quickly has me second guessing myself lol. New injectors and coil packs alone will be a significant chunk of change…Not to mention the 4L80E that I still need to source.

Cylinder Bore Measurements

Piston 1
Thrust - Top 0.0030 / Middle 0.0025 / Bottom 0.0015
Non Thrust - Top 0.0005 / Middle 0 / Bottom 0.0005
Piston 2
Thrust - Top 0.0020 / Middle 0.0020 / Bottom 0.0015
Non Thrust - Top 0.0005 / Middle 0.0005 / Bottom 0.0005
Piston 3
Thrust - Top 0.0020 / Middle 0.0020 / Bottom 0.0015
Non Thrust - Top 0.0005 / Middle 0 / Bottom 0.0005
Piston 4
Thrust - Top 0.0020 / Middle 0.0015 / Bottom 0.0015
Non Thrust - Top 0.0005 / Middle 0 / Bottom 0.0005
Piston 5
Thrust - Top 0.0020 / Middle 0.0020 / Bottom .0015
Non Thrust - Top 0.0010 / Middle 0.0005 / Bottom 0
Piston 6
Thrust - Top 0.0020 / Middle 0.0020 / Bottom 0.0015
Non Thrust - Top 0.0005 / Middle 0.0005 / Bottom 0.0005
Piston 7
Thrust - Top 0.0020 / Middle 0.0020 / Bottom 0.0015
Non Thrust - Top 0.001 / Middle 0.0005 / Bottom 0.0010
Piston 8
Thrust - Top 0.0035 / Middle 0.0030 / Bottom 0.0020
Non Thrust - Top 0.0010 / Middle 0.001 / Bottom 0.0005

Jake Wade

Those measurements are above 4.00 correct?

The pistons when new should measure around 3.9985-3.999. With your bores measuring as much .0035 over 4.000, your actual piston to bore clearance is more like .0045-.005 assuming zero wear on the skirts.

I have re-ringed Gen 3 engines under this same scenario and had no issues BUT, these were just low rpm daily driver truck stuff.

In your case, I’d probably spend the money on a bore and new pistons but, people get away with boosted builds straight out of the yard all the time.

92SierraSLE

Thanks for the reply Jake. Correct, all measurements are above 4.00.

Fast355

Time to bore it. Your cylinders are egg shaped and tapered like an ice cream cone. Neither are good for ring seal. The more cylinder pressure, the more blowby and lost power.